Agricultural machines towed by a tractor across a field for picking up windrowed crop material to form a cylindrical bale are commonly referred to as round balers. These machines have either a fixed or an expandable bale forming chamber disposed between opposing vertical sidewalls. The chamber is usually defined by a floor and transverse confining means comprising a continuous flexible apron and/or a plurality of transverse rolls. Frequently the apron includes an array of side-by-side belts trained around a series of rollers that extend between the sidewalls, and the floor consists of either a large roller or a continuous conveyor belt.
During field operation, crop material such as hay is picked up from the ground and fed into the chamber. The volume of crop material increases continuously in the chamber until a compact cylindrical package is formed. The package is wrapped while still in the chamber and then ejected onto the ground as a completed bale.
Well known means for wrapping round bales include twine, net and plastic sheet material. When twine is used it is common to utilize a tube to dispense twine along the circumference of the formed package as it is being rotated in the chamber to helically wrap a continuous strand of twine around the bale. The twine tube is moved to feed out twine along a transverse path adjacent the outer surface of the cylindrical package as it is being turned in the chamber. Twine wrapping apparatus of this type is shown in U.S. Pat. No. 5,215,005, issued Jun. 1, 1993 in the name of Stephen C. Schlotterbeck, et al.
When a sufficient amount of twine has been wrapped around the package the twine is cut, typically by guiding the twine to a stationary cutting mechanism which severs the strand by either a positive cutting action or by pulling it against a fixed cutting edge. Referring again to Schlotterbeck, et al, a stationary cutting mechanism is shown wherein the twine being dispensed is guided across a fixed striker plate and continues to feed out until a knife edge is thrust against the striker plate to severe the twine.
U.S. Pat. No. 4,440,075, issued Apr. 3, 1984 in the name of Melvin V. Gaeddert, also shows a round baler having a stationary cutting mechanism. The twine is guided to the cutting mechanism and severed by pulling it against an exposed cutting edge.
In another prior art arrangement, shown in U.S. Pat. No. 4,505,197, issued Mar. 19, 1985 in the name of Paul S. Shenberger, et al, the twine cutting mechanism includes a swinging arm that engages the twine and pulls it against a knife. The arm in this device also serves to clamp the supply end of the twine after it is severed.
Another known approach in the round baler prior art is the use of a cutting mechanism that is not stationary. U.S. Pat. No. 4,715,175, issued Dec. 29, 1987 in the name of Siegfried Schaible, et al, shows round bale wrapping apparatus in which a cutting mechanism is slideably moved to its cutting position after the wrapping operation is completed.
As in all aspects of round balers, reliability is a very important factor in the twine cutting operation. Serious problems are encountered if the cutter fails, i.e., the twine has not been severed prior to ejection or is some instances the twine continues to feed out long after a sufficient amount of twine has been wrapped around the package of crop material. Due to the location of many prior art cutting mechanisms in an environment that is inherently dusty, failures occur due to build up of dirt and debris in the vicinity of the twine strand to be cut, causing the cutting edge to be blocked from contact or to make improper contact.